1. Field of the Invention
The present invention relates to a lens barrel and an optical apparatus including the lens barrel.
2. Description of the Related Art
Hitherto, an image taking lens used in an optical apparatus such as a single-lens reflex camera is required to have advanced functions at a high zoom ratio (high magnification ratio) that exceeds 5×. For example, an image taking lens is required to have an autofocus function. From the viewpoints of increasing speed, silencing noise, and increasing precision, an autofocus actuator is required to be an annular oscillating-wave motor that rotates around an optical axis. As other functions, an image taking lens is required to have an image blur correcting mechanism for restricting image blur caused by hand shake.
In addition, for further increasing convenience, there is a demand for reducing the size of the entire lens barrel. In general, in order to obtain a high zoom ratio in a zoom lens, it is effective to increase a moving-out amount of a lens unit that is closest to an object side (hereunder referred to as the “first lens unit”). However, when an attempt is made to provide the aforementioned functions or to reduce the size, the moving-out amount of the first lens unit cannot be made large.
Japanese Patent Laid-Open Nos. 2005-77425 and 2001-318292 each discuss a lens barrel of a zoom lens whose zoom ratio is increased by moving out a moving-out mechanism of a first lens unit in two or more steps.
Japanese Patent Laid-Open No. 2005-77425 discusses a structure of the lens barrel in which the moving-out amount of the first lens unit is made large by a first cam cylinder disposed inwardly of a first stationary cylinder, a second cam cylinder disposed inwardly of the first cam cylinder, and a cam groove provided at the inner periphery of a first lens unit moving cylinder. In this structure, if the first cam cylinder is rotated by a zoom operation, rotation is transmitted to the second cam cylinder by mutual action between a straight groove of the first cam cylinder and a roller provided at the second cam cylinder.
However, in the lens barrel discussed in Japanese Patent Laid-Open No. 2005-77425, if an attempt is made to mount the aforementioned annular actuator as a driving unit of the lens unit, the length of the first lens unit moving cylinder in the direction of an optical axis is restricted. Therefore, a sufficient moving-out amount of the first lens unit moving cylinder cannot be easily provided. In addition, since a cam cylinder 1 and a cam cylinder 2 are disposed inwardly of the stationary cylinder, if an attempt is made to mount the aforementioned image blur correcting mechanism, the image blur correcting mechanism needs to be disposed in a narrow space situated inwardly of the cam cylinder 2. This makes it difficult to mount a mechanism that can provide a sufficient image blur correction effect.
Japanese Patent Laid-Open No. 2001-318292 discusses a structure of the lens barrel in which the moving-out amount of a first unit cylinder is made large by a first cam cylinder disposed outwardly of a stationary cylinder, a thrust ring disposed outwardly of the first cam cylinder, and a third cam cylinder rotatable relative to the thrust ring. In this structure, if the first cam cylinder is rotated by a zoom operation, its rotation is transmitted to the third cam cylinder by mutual action between a roller provided at an end of the first cam cylinder and a straight groove of the third cam cylinder.
However, even in the lens barrel discussed in Japanese Patent Laid-Open No. 2001-318292, if an attempt is made to mount the aforementioned annular actuator as a driving unit of the lens unit, the length of the third cam cylinder in the direction of an optical axis is restricted. Therefore, a sufficient moving-out amount of the first unit cylinder cannot be provided. In addition, if an attempt is made to provide a sufficient moving-out amount of the first unit cylinder by increasing the length of the third cam cylinder, the transmission of rotation between the first cam cylinder and the third cam cylinder is limited. Therefore, the movement amounts of the thrust ring and the third cam cylinder cannot be made large. Consequently, when the cam cylinder 3 is made longer towards an object side, the shortest overall lens length is increased.